Apparatus for polishing samples

ABSTRACT

IN AN APPARATUS FOR POLISHING METALLOGRAPHIC SAMPLES MOUNTED IN CYLINDRICAL HOLDERS, A STATIONARY DISC IS MOUNTED ABOVE A ROTARY POLISHING WHEEL, WHICH DISC HAS A SYSTEM OF SLOTS AND GUIDE RAILS FORMING A CLOSED STAR-LIKE PATH IN WHICH SAMPLES RESTING FREELY ON THE POLISHING SURFACE ARE CAUSED TO ROLL ALTERNATELY OUTWARDS AND INWARDS BY ENGAGEMENT OF THE SAMPLE HOLDERS WITH THE GUIDE RAILS AND THE WALLS OF THE SLOTS.

. Feb. 9, 1971 K. A. GEELS I APPARATUS FOR POLISHING SAMPLES 2 Sheets-Sheet 1 Filed June 18, 1968 I Fig.2

I N VENTOR M M 3 J H201 V Q, [W 1 J l wk V//////.//, m V W IIVI ATTORNEY Feb. 9, 1971 6 K. A. GEELS 3,561,166

' APPARATUS FOR POLISHING SAMPLES Fild June 18,1968 2 Sheets-Sheet 2 INVENTOR ATTORNEY 3,561,166 APPARATUS FOR POLISHING SAMPLES Kay A. Geels, Copenhagen-Valby, Denmark, assignor to H. Struers Chemiske Laboratorium, Copenhagen, Den- Filed June 18, 1968, Ser. No. 738,032 Claims priority, application Germany, June 19, 1967, St 27,023 Int. Cl. B24b 5/00 U.S. Cl. 51-129 1 Claim ABSTRACT OF THE DISCLOSURE In an apparatus for polishing metallographic samples mounted in cylindrical holders, a stationary disc is mounted above a rotating polishing wheel, which disc has a system of slots and guide rails forming a closed star-like path in which samples resting freely on the polishing surface are caused to roll alternately outwards and inwards by engagement of the sample holders with the guide rails and the walls of the slots.

BACKGROUND OF THE INVENTION The invention relates to an apparatus for polishing samples, The word polishing as used herein is to be taken in a wide sense so as to comprise any form of mild abrasive treatment, thus, e.g., also grinding by means of grinding paper. The apparatus has principally been developed for metallographic purposes and will therefore be particularly described for this use. The pieces to be polished are therefore referred to as samples, though they may of course also be workpieces of similar shape and size as metallographic samples.

It is known to treat a plurality of metallographic samples simultaneously on a horizontal rotating polishing Wheel, the samples being mounted in a rotating sampleholding frame, which imparts to the samples a circular movement excentric to the axis of rotation of the polishing wheel. It is also known to impart to the individual samples an individual rotary motion relative to the sample holding frame. By such arrangements it is attempted constantly to change the polishing direction relative to the surface of the sample so as to avoid smearing of the constituents of the samples in a certain direction and also to avoid that a limited harder or a softer constituent might cause surface portions immediately succeeding the said limited area in the polishing direction to be subjected to a treatment different form that of other surface portions. Moreover, brittle constituents such as graphite are better preserved than if polishing were effected for a considerable period of time in the same direction.

By the simultaneous treatment of a plurality of samples with the aid of an automatic sample-holding frame a saving of labor is obtained, and the polishing will be independent of the different ability of different operators. The necessary polishing pressure may be obtained by providing the sample-holding frame with weights, which load the individual samples by way of pressure rods. The individual samples may then be individually inserted and removed and have the freedom of adjusting themselves into full engagement with the surface of the polishing wheel.

' United States Patent 0 3,561,166 Patented Feb. 9, 1971 Similar advantages are obtained by the so-called vibration polishing devices, in which samples loaded by weights rest freely on a vibrating polishing wheel. Various systems have been proposed for the vibratory motion of the polishing wheel, A common feature is that the vibrating motion is a complex motion, by which the samples are caused to perform both a sliding motion relative to the polishing wheel and a rotary motion about their own axes. In this manner excellent polishing results are obtainable, but the polishing speed is rather low.

It is the object of the invention to provide an apparatus, which is simpler than the first-mentioned polishing apparatus and still fulfills the requirement of a uniform polishing in constantly changing directions, and which on the other hand permits faster polishing and better economy than the last-mentioned polishing apparatus.

It is known per se that samples that rest freely on a rotating horizontal polishing surface and are mounted in cylindrical holders or otherwise equipped with a circular rolling surface can be caused to rotate by means of a stationary cam face engaged by the said circular rolling surface. However, it has not yet been found possible to utilize this phenomenon in a rotational manner so as to enable the simultaneous placing on the polishing surface of a sufiiciently large number of samples to make the polishing procedure economically competitive and at the same time to obtain a fully controlled smooth rotation of the samples about their own axes during the whole duration of the treatment.

SUMMARY OF THE INVENTION To solve this problem, according to the invention, an apparatus for polishing samples comprises a rotatable polishing wheel with a vertical axis and a horizontal polishing surface, and stationary cam means above said polishing surface for the guiding of samples resting freely on the polishing surface and equipped with a circular rolling surface for engagement with said cam means, said cam means comprising a system of cam faces defining for the sample axes, within the circumference of the polishing surface, a path of movement having alternate portions running outwards and inwards respectively and being oppositely inclined to radial direction.

In the substantially star-shaped path of movement thus defined a great number of samples may be present at the same time, and these samples will be entirely independent of one another so that it is not necessary to insert dummies if a smaller number of samples or maybe just one sample is to be treated at a time. The rolling movement of the samples is caused by the fact that, by virtue of the inclination of the alternate portions relative to radial direction, the resultant of the frictional forces acting on the samples as a consequence of the polishing treatment will always intersect the cam faces in a point spaced from the point of engagement between the rolling surface of a sample and the cam surface, viz., outside the said point of contact along one cam face and inside the said point of contact along the succeeding cam face. Thereby the samples are automatically caused to roll along the cam faces under the influence of the polishing forces so that the polishing direction is constantly changed. The rolling speed may be adjusted as desired by suitably selecting the shape of the cam faces. Preferably, the said rolling speed should be kept small relative to the speed of the polishing motion.

Like in the known apparatus, the polishing surface usually consists of a polishing cloth placed on a polishing wheel and having a suitable abrasive applied thereto. The abrasive may, e.g., be a thin dispersion of aluminium oxide, but it is also possible to use a diamond paste, if desired in combination with a lubricating agent. Depending on the type of friction between the samples and the polishing surface viz. fluid, semi-fluid or dry, the frictional resistance against the rolling motion varies more or less or not at all with the speed of the rolling motion. The shape of the cam faces should preferably be so selected that a state of equilibrium is established between the rolling force, which is substantially determined by the instantaneous angle between the polishing direction and the cam face on one hand and the frictional resistance against the rolling motion on the other hand so that the rolling of the sample along the cam face takes place at a reasonably constant velocity. It has been found that in the case of fluid or semi-fluid friction the said condition can be fulfilled with an accuracy sufiicient for practical purposes, if the portions of the path and movement defined by the cam faces are substantially straight lines which are off-set from the axis of rotation of the polishing wheel.

In a construction of this type, a particularly good utilization of the polishing surface is obtained when successive outwardly and inwardly directed portions of said path of movement are substantially parallel and located on opposite sides of a radius substantially parallel to both.

To obtain a path of movement of the last named type, the cam means may, according to a preferred embodiment of the invention, comprise a disc having a plurality of angularly spaced substantially rectilinear slots merging at their inner ends and closed by substantially semi-circular end walls at their outer ends, and a plurality of narrow guide rails extending substantially along the medium planes of said slots and having their outer ends located substantially at the centers of said semi-circular end walls and merging into each other at their inner ends along rounded transitional portions.

Like in the known apparatus, the samples are preferably loaded by means of weights, which weights may be constructed as sample holders, in which the samples are mounted. According to the invention, the circular rolling surfaces of the samples may then be constituted by annular faces of the sample holders, the said annular faces engaging the cam faces.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a horizontal section through an apparatus according to a preferred embodiment of the invention along the line II in FIG. 2,

FIG. 2 is a section along the broken line 11-11 in FIG. 1, and

FIG. 3 a diagrammatic illustration of part of the path of movement of a sample.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing, 1 is a horizontal rotating polishing wheel, which is constructed with an upstanding marginal edge 2. The polishing wheel is provided with a polishing cloth 3 and the recess formed within the marginal edge 2 is partly filled with a dispersion of a polishing agent, such as aluminium oxide. It is also possible to apply diamond paste to the polishing cloth 3 or to place a polishing or grinding paper on the polishing wheel.

A stationary disc 4 is mounted above the polishing wheel and is constructed with a number of rectilinear slots 5, which are off-set from the axis of rotation of the polishing wheel. The slots 5 merge at their inner ends and are closed by substantially semi-circular end walls 11 at their outer ends.

A narrow guide rail 6 is provided in each of the slots 5. The guide rails are mounted on a common hub 12 and extend substantially to the centers of the semi-circular end walls 11. The guide rails 6 are also off-set from the axis of rotation of the polishing wheel. At a distance above the polishing wheel sufiicient to allow the samples to pass, the guide rails 6 are provided with extensions 13 which are connected with the disc 4 by means of vertical ribs 14. 8 is a sample holder, in which a metallographic sample 9 is mounted. The sample holder is constructed with an annular face 10 serving to roll along the walls of the slots 5 and the guide rails 6.

The hub 12 forms substantially semi-circular curves of transition between the guide rails 6, while the semi-circular end walls 11 form curves of transition between the edges of the slots 5.

A sample, which is placed in the passage formed between the walls of the slots 5 and the guide rails 6, will, assuming the direction of rotation of the polishing wheel to be as indicated by the arrow, first roll outwards along a guide rail 6 and will then move along the semi-circular end wall 11 to the frontmost edge of the corresponding slot 5, whereupon the sample will roll inwards along the said edge and be delivered to the subsequent guide rail 6 by way of the curve of transition 7 of the hub 12. This process is repeated in the next slot and so on, until the sample has returned through a closed path to its starting position, whereupon the whole operating cycle is repeated again and again, until the sample is removed. As will be seen, it is possible to treat as many samples at a time as can be accommodated in the closed guiding passage formed by the slots 5 and the guide rails 6. Each such sample can be individually inserted and removed at will.

In FIG. 1, the path of movement of the sample axes is indicated by a dash-dotted line. In FIG. 3, part of this path of movement is illustrated on a larger scale. ab is a portion of the path of movement running outwards, then follows a semi-circular transitional portion [2-0, and then again a portion c-d running inwards. As will be seen, the portions ab and ad of the path of movement are parallel to one another and located on opposite sides of a radius H through the axis of rotation O.

The radial direction in the points a, b, c and d is indicated by radii A, B, C and D. The inclination of the path of movement to the radial direction in any point is denoted by a, ,8, 'y and 5 for the points a, b, c and a. As will be seen, this inclination is directed upwards (i.e., forwards in the direction of rotation) for the points a and b and consequently for the whole stretch ab, while on the other hand the said inclination is directed downwards (i.e., rearwards) for the whole stretch cd.

In FIG. 3, also the annular surface 10 of a sample holder present in the point a, as well as part of a guide rail 6 are shown. The resultant of the polishing forces acting on the sample is denoted by P. It extends substantially perpendicularly to the radial direction (here A) through the center of the annular surface 10 (here a). As will be seen, the resultant P intersects the guide rail 6 in a point outside the point of contact between the annular surface 10 and the guide rail 6. The force P can therefore be dissolved into a perpendicular force N and a rolling force R directed outwardly along the path of movement.

Owing to the opposite inclination of the stretch c-d, an inwardly directed rolling force will act on a sample present in a point of that stretch.

What is claimed is:

1. An apparatus for polishing samples, comprising a rotatable polishing wheel with a vertical axis and a horizontal polishing surface, and stationary cam means above said polishing surface for the guiding of samples resting freely on the polishing surface and equipped with a circular rolling surface for engagement 'with said cam means, said cam means comprising a disc having a plurality of angularly spaced substantially rectilinear slots merging at their inner ends and closed by substantially semi-circular end walls at their outer ends, and a plurality of narrow guide rails extending substantially along the medium References Cited planes of said slots and having their outer ends located UNITED STATES PATENTS substantially at the centers of said semi-circular end walls,

the walls of said slots and said guide rails defining for the 3O77706 2/1963 Coons 51 129X sample axis a path of movement having alternate portions FOREIGN PATENTS running outwards and inwards, respectively, the outwardly o 222 184 5/1910 Germany.

and inwardly directed portions of said path of movement 83:168 11/1919 Switzerlani being substantially parallel and located on opposite sides of radius substantially parallel to both. HAROLD D, WHITEHEAD, Primary Examiner 

